This Physician Scientist Award is designed with a two-fold purpose. First to develop the applicant into a skilled researcher with experience in basic scientific research and secondly to expand existing knowledge of the specific physiologic response of trabecular bone to an orthopaedic implant model of known mechanical stress. Trabecular bone has an important relationship to orthopaedic implants in total joint arthroplasty. Most work on bone response and remodelling has dealt with cortical bone. In total joints, the stresses may be passed directly to trabecular bone, and its response to this stress may have a great deal of effect on loosening, the dominant factor in implant failure. Work currently under way has shown a definite change in trabecular bone response with time and type of mechanical stress. To the simplest observations, this response has included changes in trabecular size and orientation. A careful description of the physiologic response of trabecular bone to an applied stress at the cellular level is lacking and needed to further our understanding. These same studies need to be undertaken in osteopenic bone to more fully simulate the trabecular response of the elderly total joint population. This is the focus of the second phase of this proposal and includes detailed microscopic and histochemical analysis of the bone. In a constantly aging society with known loss of trabecular bone substance, these responses may contain valuable clues both to prevent implant loosening, and arrest or reverse trabecular bone loss.